The most recent prior art in connection with rotary pumps is disclosed in commonly owned U.S. Pat. No. 5,370,514, to Morita et al.
The prior art structure is discussed hereinafter in detail to facilitate clear understanding of the improvements of the present invention.
FIGS. 10 and 11 show the commonly owned prior art. In these drawings, rotors 1A and 1B from a short rotor shaft 2 is provided from the central portion of one end surface thereof. A threaded bore 3 is coaxially formed from the end surface of the rotor shaft 2. A pumping segment 4 is integrally formed on the outer peripheral portion of each rotor 1A and 1B.
A pump casing 6 includes a main casing defining a concave 25 pumping chamber 7 loosely accommodating the pumping segments 4 or revolution therein and formed with a suction port 8 and a discharge port 9, and a casing cover 11 detachably attached on a main casing 10 flush with the end surface of each rotor 1A and 1B by bolts and nuts.
Hollow rotor drive shafts 12A and 12B are provided corresponding to the rotors 1A and 1B. The rotor drive shaft 12 is supported by a bearing 14 within a gearbox 13 for the drive shaft, for rotation and for restricting movement in an axial direction. A rotor fastening bolt 15 is inserted through a hollow portion of each of the hollow rotor drive shafts 12A and 12B from one end to the other end. A bolt head 15a of the rotor fastening bolt 15 is engaged with one end surface of the rotor fastening bolt 15.
A hollow portion 16a at the tip end of each rotor drive shaft 12A and 12B is externally engaged with the rotor shaft 2 of each rotor 1A and 1B.
In conjunction therewith, a threaded portion 15b at the tip end of the rotor fastening bolt 15 is threadingly engaged with the threaded bore 3 of the rotor shaft 2.
A gearbox 17 for a transmission shaft is shown in FIG. 11. A transmission shaft 21 is rotatably supported in bearings 18 and 19 within the gearbox 17, and is connected to a motor (not shown). A gear 22 is mounted on the transmission shaft 21. In the gearbox 13 for the drive shaft, gears 23a and 23b are mounted for transmitting rotation to drive a pair of rotor drive shafts 12A and 12B in mutually opposite directions in synchronism with each other and a gear 23c is provided meshing with the gear 22 mounted on the transmission shaft 21. Accordingly, a driving force of the motor to be transmitted to the transmission shaft 21 is transmitted to one rotor shaft 12A through the gears 22 and 23c. The driving force of the rotor drive shaft 12A is transmitted to the other rotor drive shaft 12B through the gears 23a and 23b. 
For assembling the rotary pump constructed as set forth above, the pumping segment 4 of each rotor 1A and 1B is received within the pumping chamber 7 of the main casing 10. In conjunction therewith, each rotor shaft 2 is engaged with the hollow portion 16a at the tip end of the hollow rotor drive shaft 12 supported within the gearbox 13. Then, the rotor fastening bolt 15 is inserted within the rotor drive shaft 12 from one end to threadingly engage the threaded portion 15b at the tip end thereof with the threaded bore 3 of the rotor shaft 2. Then, the bolt head 15a is rotated by a rotary tool, such as spanner or the like for tightening to draw each rotor 1A and 1B toward the rotor drive shaft 12 for fixed fastening.
In the rotary pump assembled as set forth above, a rotational torque of the not shown motor is transmitted to the transmission shaft 21. Both of the rotor drive shafts 12 driven to rotate through the transmission shaft 21 drive to rotate both rotors 1A and 1B in mutually opposite directions in synchronism with respect to each other as shown by arrows in FIG. 11. Thus, by action of the pumping segments 4 rotated within the pumping chambers 7, liquid is sucked into the pumping chamber 7 through the suction port 8 and is pressurized and fed to the discharge port 9. In this case, overall inner side surface of the casing cover 11 is a flat surface in flush with the external end surface of the rotors 1A and 1B not to form a recessed portion between the rotors 1A and 1B. Therefore, there will be no retention of the transported liquid flowing through the pumping chamber 7. Accordingly, washing of the pumping chamber can be easily performed.
On the other hand, upon disassembling the rotors 1A and 1B, nuts 20 are loosened to remove the casing cover 11, and thereafter, the rotors I A and 1B are easily disassembled by simply loosening the rotor fastening bolts 15.
As is clear from the construction, in the prior art, the gearbox 17 for the transmission shaft 21 is provided separately from the gearbox 13 of the drive shaft, and driving force has to be transmitted to the rotor drive shaft 12 through the gear mounted on the transmission shaft 21 on the side of the motor and the gear 23a housed within the gearbox 13 for the drive shaft.
Conventionally, there are required in addition to a pair of rotor drive shafts 12A and 12B for driving the rotor as set forth above, the transmission shaft 21 for transmitting the rotational torque of the motor to the rotor drive shafts 12A and 12B, a total of at least three shafts in total. Therefore, the construction is inherently complicate.
On the other hand, as can be clear from the construction set forth above, in the recent prior art, the rotor fastening bolt 15 inserted into the hollow portion of the hollow rotor drive shaft 12 is rotated by rotating the bolt head 15 at the rear end with the rotary tool so that the threaded portion 15b at the tip is threadingly engaged with the rotor 1A(1B) to draw the rotor 11A backward by the rotor fastening bolt 15 and to abut the bolt head 15a onto the end surface of the hollow rotor drive shaft 12. On the other hand, upon disassembly, the rotors 1A and 1B can be disassembled easily only by loosening the rotor fastening bolt 15 by rotatingly operating the bolt head 15a. Also, the mating surfaces of the rotor 1A(1B) and opposing casing cover 11 may be formed flush. Coupling between the rotor 1A(1B) and the hollow rotor drive shaft 12A(12B) is effected by externally engaging the tip end of the drive shaft and by maintaining external engagement by drawing force applied by tightening the rotor fastening bolt 15 into the rotor shaft 12. Therefore, the force of the connection between them is insufficient. Also, centering of the rotor 1A(1B) and the hollow rotor drive shaft 12A(12B) cannot be complete thereby to cause possible center vibration.
Furthermore, as shown in FIGS. 10 and 11, the conventional rotary pump defines the pumping chamber 7 with the main casing 10 and the casing cover 11 mounted thereon. A pair of rotors 1A and 1B are housed within the pumping chamber 7. The end surface 1a of the casing cover 111 of each of rotors 1A and 1B are placed in substantially contacting state with a minimum fine gap required for permitting rotation of the rotors 1A and 1B. Both rotors 1A and 1B are synchronously rotated in mutually opposite directions by mutually engaging the pumping segments 4 of the rotors 1A and 1B by the rotor drive shafts 12 as shown by the arrows of FIG. 11. Thus, the liquid is sucked into the pumping chamber 7 through the suction port 8, and pressurized and fed to the discharge port 9. In this case, a gap between the end surface 1a of each rotor 1A and 1B and the inner surface 11a of the casing cover 11 mating thereto are substantially in contact with a minimal fine gap for permitting rotation of the rotor 1A and 1B. The ability to flow of the liquid in this fine gap is quite low. Accordingly, even when washing liquid is circulated within the pumping chamber at the end of workday, the washing liquid does not flow sufficiently between both surfaces 11a and 1a. Therefore, a sufficient washing effect cannot be achieved.